Despite increased sophistication in measurement of PTSD, little is known about the long-term longitudinal course of this disorder or the fluctuation of symptoms over time. Because previous studies have focused on the development and persistence of symptoms immediately following a stressor, the course of the chronic disorder has been largely unexplored. Although there is evidence of both persistence and fluctuation of PTSD symptom presentation in Vietnam veterans, little is known about how much and in what ways symptoms change over time. This investigation will increase understanding of the nature and extent of symptom fluctuation as well as the longitudinal course of PTSD as first steps in determining which variables affect that course and how clinicians might intervene to alter it.